The present invention relates to a system for controlling cooling water temperature for an engine mounted on a vehicle and more particularly to a system which controls the temperature of the cooling water to a proper temperature according to load on the engine and operation of a heater for a room of the vehicle.
Japanese patent publication No. 54-9665 discloses a cooling water control system which is provided with two thermostats for low temperature control and high temperature control. The system has disadvantages that the two thermostats occupy a large space and that the cooling water temperature is unsufficiently controlled for the heater which causes decrease of heating efficiency in heavy load condition. Generally, the heater system of the vehicle uses the cooling water. Accordingly, it is necessary to control the cooling water temperature for heating effect.